The present invention concerns a solar simulator, especially a solar simulator that is usable for measuring solar cells.
Solar simulators serve to simulate natural sunlight in order to be able to investigate the effects of sunlight on certain objects to be irradiated. A special application is the examination of the performance of solar cells.
Such solar simulators are, for example, known from U.S. Pat. No. 4,641,227. There, a simulation of sunlight is realized through a suitable arrangement that filters two independent sources of radiation, and subsequently superposes the radiations coming from these radiation sources. Nonetheless, the relatively high construction expenditure of the radiation sources"" arrangement as well as of the optical system is disadvantageous. Also, the variation breadth of the radiation generated through the given optical system is relatively small.
There is therefore needed a simplified and variable solar simulator arrangement. This need is met by providing a solar simulator having a radiation source for generating radiation with a spectral (energy) distribution that largely corresponds to the spectral distribution of sunlight. At least one filter is arranged in the region of the radiation source. This filter suppresses long wave or short wave radiation components of the radiation source. The filter is movable, basically perpendicular, to the irradiation direction of the radiation source. An irradiation plane capable of accommodating objects to be irradiated is set at a distance from the radiation source and the at least one filter such that the radiation coming directly from the radiation source, as well as the at least one filter, impinge on the irradiation plane as basically homogenous radiation of a punctiform light source.
The solar simulator of the present invention has the following: a radiation source for generating radiation with a spectral distribution which largely corresponds to the spectral distribution of sunlight; at least one filter arranged in the region of the radiation source which suppresses long wave or short wave radiation components of the radiation source and is arranged movable, basically perpendicular, to the irradiation direction of the radiation source; and an irradiation plane with facilities for accommodating objects to be irradiated which is set at a distance from the radiation source and the at least one filter such that the radiation proceeding directly from the radiation source as well as the at least one filter impinge on the irradiation plane as basically homogenous radiation of a punctiform light source.
Consequently, in contrast to the state of the art, only a single radiation source is required, which basically simplifies the arrangement. Owing to at least one movable filter, the composition of radiation, thus the components of long wave and short wave radiation components, can be varied in a relatively wide range, and the desired radiation spectrum can be optimally adjusted. Since the irradiation plane is nevertheless so arranged that the radiation source and the radiation passing through at least one filter can practically be viewed as a single point source, one obtains, despite this, a homogenous irradiation on the irradiation plane and not an imaging of the radiation source and filter which could lead to a locally different radiation spectrum.
In particular, the radiation (light) source can be constructed as a flash lamp, for example, as a xenon flash lamp.
In order for the radiation source to develop the action of a point source, it is especially provided that the distance between the radiation source and the filter corresponds to the order of magnitude of the radiating electric arc or lamp or other radiating facility which serves as a radiation source. One possibility for realizing a homogenous irradiation on the irradiation plane is for the distance between the irradiation plane and the radiation source to come to at least 50 times, preferably at least 100 times, the distance between at least one filter and the source of irradiation.
For a special use of the solar simulator for measuring solar cells, it can be provided that a solar cell to be measured is arranged on the irradiation plane and that, moreover, additional reference solar cells are arranged on the irradiation plane for comparative measurements. In this way, the same irradiation acts on the reference solar cells as upon the solar cells to be measured in each case. For example, the solar cells to be measured can be constructed such that at least a first solar cell layer is arranged over a second solar cell layer, whereby the solar cell layers have a different absorption behavior. Such solar cells are especially familiar as dual junction solar cells or also as multi-junction solar cells. The reference solar cells are then formed by at least a first reference solar cell layer with one absorption behavior, which corresponds to at least a first solar cell layer. It is also formed by at least a second reference solar cell layer adjacent to the first reference solar cell layer, the absorption behavior of which corresponds to the second solar cell layer, whereby a filter which corresponds to the absorption behavior of the first solar cell layer is placed in front of the second reference solar cell layer. The reference solar cell layers are in this way independent from one another, but they nonetheless simulate the circumstances within solar cells arranged one above another, which are to be measured.
In order to be able to vary the radiation spectrum occurring on the irradiation plane even further, it can be provided that at least two filters are basically arranged movable perpendicular to the direction of irradiation, whereby the filter is constructed such that they suppress different radiation components in any given case. In this way, a superposition of radiation components, which have not passed through any filters, with radiation components which have passed through the first filter and irradiation components which have passed through the second filter or even additional filters now results as an overall spectrum. Making the filters slide one over the other results also in additional irradiation components that have first passed through a first filter and then a second, or still further filters.